Hmm,
 
I have just upgraded from a 6-core AMD Phenom II 1100T to the new 8-core Piledriver based FX 8350.
 
With the 1100T, it was easy to see in task manager that Sonar was using all 6 cores.  With the FX 8350, even with huge projects with dozens of FX, task manager only ever shows 4 of the 8 cores in use.  This is with both Sonar X1 and X2.  There seems to be nothing I can do to get more cores working.
 
Sonar's own CPU meter shows one core very busy and the others lightly loaded.  Task manager shows 4 of the 8 cores loaded quite similarly.
 
Other multithreaded apps seem to push all the cores.
 
Anyone else with a Piledriver CPU and Sonar who can test this?

Check: http://forum.cakewalk.com/tm.aspx?m=2095428 Also try turning off power saving features such as PowerNow! in the BIOS. Cheers...

Thanks for the reply. I should have added that I have already tried setting ThreadSchedulingModel to 2. I will have a look in my BIOS, but certainly never had to for the previous 6-core. And as said, other apps are taxing all cores.

Turns out that these MS hotfixes solved my problem.  All cores now fully engaged!

Let me just add here that if you have a Phenom II 6-core and you've been wondering of the FX 8350 is a good move for Sonar, I think the answer is a resounding YES.

I have a project loaded with massive numbers of FX that I use as a Sonar-killing test.  Until tonight, I have never been able to drop below 128 buffers without bad distortion.

I've just tested it at 64 buffers on the FX 8350 with the hotfixes mentioned above, and it is just crusing through my test without so much as a glitch.

If you have an AM3+ board, this is a no-brainer upgrade for Sonar.